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Climate Hustle

Infographic: 97 out of 100 climate experts think humans are causing global warming

Posted on 11 May 2011 by John Cook

I was talking about climate to my dad last week (since the book launch, he will now talk to me about the subject) and I mentioned that 97% of climate scientists are convinced that humans are causing global warming. He registered great surprise at that statistic. "I thought it was more 50/50", he said. It made me realise just how good a job both the mainstream media and the fossil fuel funded disinformation campaign have done in confusing the public about the scientific consensus on global warming. At the same time, I was working on a consensus graphic (cribbed from the Guide to Skepticism) for a video presentation. So as a tool for anyone wishing to communicate the scientific consensus, I've added the following infographic to the Climate Graphics resource:

The 97% figure comes from two independent studies, each employing different methodologies. One study surveyed all climate scientists who have publicly signed declarations supporting or rejecting the consensus (Anderegg 2010). Another study directly asked earth scientists the following question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" They found 97% of actively publishing climate scientists answered yes (Doran 2009). As "climate scientists actively publishing peer-reviewed research on climate change" doesn't really roll off the tongue, I abbreviated that down to "climate experts".

One feature of Doran's survey results is that while 97% of climate expert said "yes, humans are causing global warming", only 1% said "no, we're not". The other 2% were unsure:


Response to the survey question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (Doran 2009)

I've indicated the "I'm not sure" portion in the "97 out of 100 climate experts" infographic with grey colouring.

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Comments 201 to 219 out of 219:

  1. I see no reason to expect the climate uncertainty to be skewed towards the high end. One should read some of the papers presented by KR at 188, which includes the Annan and Hargreaves work.

    The papers which base their calculation of climate sensitivity on temperature data indicate a lower value. The Padilla paper list 2.0 as the most likely value. Modeling methods consistently yield higher values. There is some question as to the validity of incorporating the paleoclimate data as conditions differed greatly from the present.

    I see no evidence for a tightly centered range close to three. On the contrary, the range is rather broad, with each line of evidence generating sub peaks and curves within the larger range.

    Risks assessment may be useful for political and insurance purposes, but should not be incorporated in this scientific analysis. I would not advise anyone to ignore scientific practices and accept a questionable value for anything. I do not know why you would. Based on the previous analyses, there is less than a 50% chance that the climate sensitivity falls between 2.5 and 3.5.

    Why would politicians bet on high or low climate sensitivity in the first place?
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  2. Public policy in the face of incomplete data/understanding is a bet which needs to incorporate most likely and also the precautionary principle. At the moment, policy (do nothing) appears to be gambling on sensitivity less than 2 (less than 1 even), which fails in both regards. Me, I would bet on the sensitivity of the models which most accurately track temperature trend on 30 year cycle over period where we have reasonable accurate temperature and forcing data.
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  3. Actually Tom, I find the opposite to be true. There are clusters of values depending on the method used; models tend to yield higher values, temperature data lower, etc., resulting in several peaks within the distribution.

    KR presented a nice listed of climate sensitivity studies in #188. Those that used primarily CO2 to determined climate sensitivity arrived at the highest values as the Sanderson paper had a range of 2.45 - 7.32 and Hergerl 1.5 - 6.2. Those that incorporated higher natural components arrived at much lower estimates; Schneider 1.08 - 2.3 and Harvey 1 - 2. In some of these studies the most likely value was less than 2, in other it was greater than 4. To accept a mean value at this point is unwarranted, as it has a high probability of being wrong by more than 0.5C.

    Risk management may be fine for politicians and insurance agents, but is fruitless in scientific work. I would advice politicians, or anyone else, to bet on any value for climate sensitivity, either high, low, or middle.
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  4. 203, Eric the Red,
    Risk management may be fine for politicians and insurance agents, but is fruitless in scientific work.
    I think that this is the biggest point of contention for me. We're not talking about cold, pure science. We're not trying to discover the double helix, or riddle out quantum theory in a purely abstract detached-search-for-knowledge sense.

    Your (as in you, personally) understandings and decisions are going to affect the course of civilization. This is not abstract. This is not trivial.

    This is, in every sense of the word, risk management. It is one thing to arrive at a logically consistent conclusion that there is no risk. It is another to irrationally and arbitrarily minimize that risk, dismissing it as inconvenient.

    You be the judge of where you lie in that spectrum, but the mere fact that you don't even choose to recognize it as a risk management issue speaks volumes.
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  5. 203, Eric the Red,

    There are clusters of values depending on the method used; models tend to yield higher values, temperature data lower, etc., resulting in several peaks within the distribution.
    I don't see this statement to be at all true, and I'm afraid I must challenge its veracity. Can you back it up by listing the studies that you believe find a most likely value for climate sensitivity of less than two, versus those greater than two?

    This sort of anecdotal contention, which is so at odds with everything that I myself have read, requires supporting evidence.
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  6. Eric the Red @203:

    First, the following are the climate sensitivity studies analysed in AR4:



    The triangles represent the most probable individual value on each Probability Density Function, but the important value, the median shown by a circle, is the value such that there is an equal probability that the true value will be above that point, or below it, given the evidence in the study. It is quite clear that for 11 out of 15 studies with a displayed median, the median is very close (within 0.5 degrees) of 3 degrees. Only one study, Andronova 2001, shows a median more than 1 degree from 3 degrees.

    It is, therefore, quite plain that combining the evidence from these separate studies will result in a median close to 3. In fact, this can be seen graphically by the region in which the curves for the cumulative probability intersect:



    The large spread of the red curves, estimates based on 20th Century data, show such estimates to be very unreliable - primarily because temperatures do not reach equilibrium which introduces an additional source of uncertainty compared to paleo studies.

    Given this data from the IPCC, I would say your contention of wide divergence is refuted unless you can show such a wide divergence in more recent studies. Please not that because of the various shapes of the PDFs, giving confidence intervals does not provide us with enough information. We need to know the median values of the PDF for each estimate.

    Second, I note that the marking feature of climate change deniers is that that all agree that we should take no expensive action against the threat of global warming. They may claim that the evidence is clear that there is no threat; or they may claim that the evidence is unclear and that therefore we should take no action. The former have at least the advantage that their position is rational, though it is flatly contradicted by the evidence. The later have neither the advantages of evidential support nor a rational position.
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  7. Eric the Red - Tom Curtis is quite correct. The recent instrumental estimates have a larger spread, and generally lower values, but are only capable of measuring the climate change that occurs in short time periods. Therefore they have a tendency to underestimate longer term climate sensitivity.

    When you have multiple independent measurements (as is the case here, as various paleo measures, modellings, and recent instrumental work are using different inputs) that each produce a similar spread of uncertainties, the uncertainty is reduced with each estimate, not amplified.

    The median values are tightly clustered around 3ºC. Probabilities of significantly lower or significantly higher values for climate sensitivity are extremely small.

    So, Eric, this makes me rather curious. You've essentially asserted (repeatedly) that we are not certain, and that more study is required. The evidence says otherwise. Why should we (in a risk management sense) not act upon the data we have? Your attitude strikes me as a "Yes, but..." form of denial, and in particular of delay of action.
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  8. I will try again, since the moderater insists it will work.

    The studies do not suggest thatthe values are centered close to 3. In fact, they suggest the opposite. Models show clustering around three, will paleo data consistently shows higher values with temperature data showing lower. There are several clusters of estimates, without a smooth distribution.

    KR linked to a nice series of climate sensitivity papers. So far, I have only read through the first two pages. Some papers show higher climate sensitivity ranges; Sanderson 2.45 - 7.32 and Hergerl 1.5 - 6.2, while others show lower; Schneider 1.08 - 2.3 and Padilla 1 - 3.2 (do not ask me how anyone can list three sig. figs. in their determinations).

    Risk analysis may be fine for policy makers and insurance agents, but makes for poor scientific study.

    I would not advise anyone to accept a mean value (3.0) or median value (2.6 or 2.8) in making decisions when such a wide range exists. It may be a good starting point, but one should realize that it could be off by a large amount.

    I do nto know why politicians should bet on low, high, or mid-range cliamte sensitivity values, as they all have a high probability of being wrong.
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  9. Eric the Red - I believe the content of your last post (you have a duplicate there, don't know which one the moderators will leave) was fully stated earlier in your previous post, or possibly this one. They certainly were not deleted.

    You've received several answers since then, with Tom Curtis's probably the clearest. Median values (not means, but the 50% median, very important in asymmetric distributions) cluster strongly at 3C, with only one of the AR4 median values more than 1C away. Recent instrumental estimates have higher variability, which isn't surprising since they won't have enough data/timeframe to clearly estimate long term feedbacks.

    When you have independent measures (different proxies, instruments, models, etc.) that all produce similar results, the uncertainty decreases with each additional estimate, not increases. 3C per doubling of CO2 is a very solid value. It would be interesting to apply Annan and Hargreaves methods for Bayesian inference to the full set of estimates, rather than just three, and see how tight a limit the full set of experiments constrains that sensitivity.

    "I don't know why politicians should bet on low, high, or mid-range climate sensitivity values, as they all have a high probability of being wrong. "

    Politicians should bet on the most likely numbers, as they have the highest probability of being right.

    Again, your attitude strikes me as a "Yes, but..." form of denial, and in particular of delay of action.
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  10. 208, Eric the Red,

    Please see my responses 204 and 205 to your post 203, which are equally applicable to your post 208, where you appear to simply say the exact same thing again.

    A detailed response from you is required in order to support your position.
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  11. Eric, with the current policy (do nothing), policymakers are betting a low sensitivity. This is neither likely nor precautionary.
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  12. The question makes my head spin. It is loose enough for a goose. What it doesn't address is what is the specific cause and how much is man resonsible. Signicant is in the eye of the beholder. 0.1F would qualify for some.

    So...... what climate scientist would think we have zero impact? Very few. We have bulldozed and burned well over 50% of the forests over the last 300 years, among other things. Of course the study doesn't go into the how much CO2 imapcts because they don't want the debate to start. It does not fit the yes/no simplicity.

    I have seen quite a few of the 97%ers squirm a bit when asked how much, or whether they buy model projections. Many tend to take a "not sure how much" and "I'll wait before I endrose a model" type positions. That is what a real scientist would say. I remember seeing a few of them on a Weather Channel Special. Can you blame them? It's not warming now.

    The guys who think we have it all figured out seem to be too young to know better. Science aint that easy

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    Moderator Response:

    [JH] Unsubstantiaed global assertions are akin to sloganeering which is prohibited by the SkS Comment Policy. Please read the Comment Policy and comply with it.

  13. 97 of 100 is poppycock. It was 75 out of 77.

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    Moderator Response:

    [JH] Any way you slice it, 97% equals 97 out of 100. 

  14. Back in 2011, DB noted on a cruzn246 post that "For the newcomers, cruzn246's last 40 comments here dating back to September 26 have all consisted of comments just like this: a derivative denial of the topic of the post, followed by other commenters chiming in to help correct the errors in his/her comments. Despite numerous pointers and links to sources, you persist in your misbeliefs. That is your right. But it is clear to all the position you come from."

    Are you prepared to actually discuss and be prepared to back your assertions? If you are just criusing by making random uninformed statements, then I suggest you stop wasting peoples time. You could begin by telling which scientists have claimed to have it all figured out and what their ages are. (Experts are usually greybeards).

    Your opening remarks are answered in opening really of the AR4 and 5 WG1 reports.Why dont you read them so you know what it is you are trying to critique> Eg see here. (CO2 1.68W/m2 versus -0.15 for landuse change). Quantified enough for you? Modellers are also actually very clear on what they can or cannot predict. Checked to see what these are or are you content repeating a straw man argument from some denier site?

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    Moderator Response:

    [JH] If cruzn426's future posts are like his last two, they will be promptly be deleted for violating the SkS Comment Policy. 

  15. If science was based on popular opinion, the earth would still be flat - and at the center of the universe.  A two-question, vaguely worded survey of scientists, regardless of their qualifications, should not be tossed around like its scientific evidence of anything.

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  16. The difference, NAFFFA (@215), is that realizing the world is a sphere is a a result of a scientific process. It was the result of careful observation. Same with the heliocentricity. Casual observation might make you think the sun revolves around the world, but it was careful scientific research that gave us the real answer.

    Climate science is the same. We now have 150+ years of careful research showing us that CO2 is the biggest control knob managing the temperature of the earth. That nearly all researchers agree with this position is not surprising, given the overwhelming body of research.

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  17. NotAFossil:

    The first step in writing a scientific paper or theses is the literature review. You are unlikely to advance the science if you don't know what it is. Knowledgable scientists base their opinions on the published literature, as well as their own work.

    Follow the links to see what the quoted studies say. Then also follow this link to the paper that was based on "The Consensus Project" work (menu item at the top of the SkS page), where the "survey" is a survey of the literature - first by looking at abstracts, then by getting feedback from the authors of papers.

    The result? The scientific literature on "global climate change" and "global warming" (the keywords in the search) is also almost universally in support of the idea that humans are responsible for over half of the recent warming.

    This is scientific evidence that knowledgable, informed scientists are largely in agreement on the basics, which refutes the alternative argument that there is still significant scientific debate on whether or not humans are having an effect.

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  18. Not to pile on too much, but not looking at public opinion but at informed opinion. Informed opinion since 2nd Century BC was that world was round.

    We now have 3 different studies with different methodologies coming to same conclusion as to the state of scientific consensus. (the lastest published result is this one which is survey of publications).

    It is absolutely given that a consensus does not make a theory correct. However, it is a myth that there is no scientific consensus. For policy makers, going with the consensus is the only rational choice. If you were ill, would you be like this guy? It's not like there is any other credible theory of climate.

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  19. NotAFossil @215 starts by saying, "If science was based on popular opinion, the earth would still be flat - and at the center of the universe."

    When you first arrive at SkS, you see a button "Newcomers Start Here".  If you follow it, it provides you with (among other things) a paragraph on good places for newcomers to start, including "Warming Indicators", "10 Human Fingerprints on Climate Change", "empirical evidence that humans are causing global warming", and then in the following paragraph, "Global Warming in a Nutshell"  and "The History of Climate Science".  The last of those also appears as a  button on the home page, as does "The Big Picture".  Of these, only the last mentions consensus at all, and that only the consensus of economists.  Rather than focussing on the consensus, they all focus on the emperical evidence which shows global warming to be real, human caused, and potentially catastrophic.

    The core of this website are the 176 rebutals to pseudo-skeptical myths about global warming.  Of those, only 14 (8%) discuss the consensus.  The rest primarilly focus on the scientific evidence for AGW (there are a few dealing with discussions of fraud).  Of course, that 8% does not represent the level of SkS interest in the consensus.  Rather, it reflects the level of pseudo-skeptic misinformation trying to persuade the uninformed that no consensus exists, even though it clearly does.  (Note, due to an idiosyncrasy of the SkS search engine, it will search draft blog posts in addition to ones actually published.  At least 1 of the 14 rebutals above is still in draft form, so is not actually part of the 176 published arguments.  Ergo, 8% is an overstatement of the actual figure.)

    From this, it is very clear that SkS realizes that it is not the consensus but the scientific evidence itself that is the real reason for accepting AGW.  They discuss the consensus only to show the false claim by pseudo-skeptics that there is no consensus, that climate scientists are heavilly divided about AGW, is in fact a false claim.

    Despite this, we repeatedly get pseudo-skeptics like NotAFossil who come in with their little slogans as if SkS ever argued that science is settled by consensus.  They show by the way the focus on the consensus issue that, not only are they arguing a strawman, but they are actively avoiding engaging with the evidence that is so copiously presented elsewhere on SkS.  

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